Independent overexpression of OsRab16A and AtDREB1A exhibit enhanced drought tolerance in transgenic aromatic rice variety Pusa Sugandhi 2

Rice (Oryza sativa L.), the staple food in South-East Asian countries, is a water-intensive crop so that its productivity is highly affected by drought, the most severe environmental stress factor. We report here the development of transgenic rice via overexpression of full length OsRab16A (driven by endogenous promoter) or AtDREB1A driven by rd29A promoter in the background of the aromatic indica rice cultivar, Pusa Sugandhi 2 (PS2) through biolistic transformation. Both the transgenes were stably introgretted in T-2 generations as indicated by the results of polymerase chain reaction (PCR). Reverse transcriptase (RT)-polymerase chain reaction (PCR) analyses showed that the expression of both the transgenes was induced by drought stress in all the T-2 transgenic plants examined, which were highly tolerant to water deficit stress during both the vegetative and reproductive stages without their morphological or agronomic traits being affected. Protein immunoblot analysis with Rab16A (= anti dehydrin) antiserum showed detectable accumulation of Rab16A protein in the transgenics in response to drought stress and exogenous abscisic acid (ABA) application. The physiological studies revealed that the expression of the transgene under drought stress in T-2 transgenics was associated with lesser shoot or root length inhibition, improved leaf relative water content, stable maintenance of chlorophyll, lesser hydrogen peroxide accumulation with higher catalase activity and an increased accumulation of the osmoprotectant proline, as compared with the wild type (WT) plants. The transgenic plants also showed significantly higher filled grain, spikelet fertility and grain yield under stressed conditions. All these findings highlighted the tremendous potentiality of both OsRab16A and AtDREB1A in conferring drought tolerance without affecting the normal phenotype and physiology of the plants. To our knowledge, this is the first report on the development of a drought-tolerant transgenic aromatic rice variety through overexpression of genes, one involved in ABA-dependent pathway (OsRab16A), while the other in ABA-independent pathway (AtDREB1A) of stress tolerance, thereby highlighting the significance of both the pathways in drought tolerance of the aromatic rice varieties.